Unlike BHs, NSs source a nontrivial scalar field in JFBD gravity, and thus BNS systems can be used to constrain \(\alpha _0\) . In this section, we use the first GW observation of a coalescing BNS—GW170817 [1]}—to constrain \(\alpha _0 \)  at the 68% (and 90%) credible levels. Though the constraint from GW170817 is not as strong as those previously quoted from other experiments, this result represents the first bound directly from the highly dynamical (orbital velocities \(v \sim 10^{-1}\) ) and strong-field (Newtonian potential \(\Phi _\text{Newt} =M/R \sim 10^{-1}\) ) regime of gravity.
